Some of us here at Google spend almost all of our time thinking about one thing: How do we create a three-dimensional model of every built structure on Earth? How do we make sure it's accurate, that it stays current and that it's useful to everyone who might want to use it?

One of the best ways to get a big project done — and done well — is to open it up to the world. As such, today we're announcing the launch of Google Building Maker, a fun and simple (and crazy addictive, it turns out) tool for creating buildings for Google Earth.

We like to think of Building Maker as a cross between Google Maps and a gigantic bin of building blocks. Basically, you pick a building and construct a model of it using aerial photos and simple 3D shapes – both of which we provide.When you're done, we take a look at your model. If it looks right, and if a better model doesn't already exist, we add it to the 3D Buildings layer in Google Earth. You can make a whole building in a few minutes.

Our early beta testers insist that Building Maker is more like a game than a tool.Check out this video to see Building Maker in action:

For now, you can choose to make buildings in any of about 50 cities. We'll keep adding more cities, but don't feel left out if we don't have your hometown yet — modeling in a place you've never been is a fantastic way to discover more about it. Teachers might find that Building Maker is a great way to get students interested in geography. Armchair tourists can not only visit an unfamiliar city; they can engage with it. It's amazing what you learn when you look at something really closely.